Automatic coin machines such as coin testers discriminate a predetermined set of coins within a very short time. In this respect, a number of processes are known, a multiplicity of which employ the coin material as a discrimination criteria. The thickness and diameter of the coin are also resorted to for discrimination. However, the worldwide currency system cannot rule out that equal or nearly equal blanks are employed for different coins. Therefore, the embossed image is an important discrimination criterion for differentiating coins.
A process and device for processing an embossed card is known from DE 37 39 239 C2. The embossed side of the card is alternately illuminated from two opposed, oblique directions. An image of the card is picked up at these different illuminations. The difference of the picked-up images is compared to reference data to identify the embossed characters. However, this process is unsuitable for intensely reflective metallic surfaces of coins.
DE 33 05 509 describes an optical coin testing device in which a surface illuminated under one angle is viewed under different angles. The quotient obtained from the brightness under different angles provides information about the degree of gloss of the coin being tested.
U.S. Pat. No. 5,839,563 describes a coin tester in which a comparison of samples is made for the picked-up image of the coin. The coin is illuminated circularly to achieve an intense illumination of the object field.
DE 100 51 009 describes a method for identifying an embossed image of a coin in which the coin is moved past the light source and is illuminated from a different direction each across two or more lighting portions. A differential image determined from these exposures indicates whether the image is a photographic reproduction of the embossed image or is an embossed image.
It is the object of the present invention to provide a process for identifying an embossed image of a coin, which is apt to reliably identify a genuine-coin or counterfeit-coin signal for the inserted coin by simple means in an automatic coin machine.